Field of the Invention
This invention relates to vegetation trimming apparatus and, more particularly, to a vegetation trimming apparatus having at least one cutting blade with a cutting edge that is moved in a reciprocating path to effect severance of vegetation.
Background Art
One well-known and successful design of vegetation trimming apparatus uses a pair of reciprocating, elongate cutting blades. Each of the cutting blades has a cutting edge. As the cutting blades move, the cutting edges cooperate to produce a scissors-type action that severs vegetation.
The cutting blades are carried on a support that projects in cantilever fashion from a frame upon which a housed drive is mounted. The housing is of a construction that a user can conveniently grasp and manipulate the same to effect controlled cutting.
The blades move within a working space between two fixed surfaces that face each other. One of the surfaces is defined by the support, with the other surface defined cooperatively by a plurality of spacer units that are provided at locations at regular intervals along the blade length. Each spacer unit is made up of a body with a head and a threaded shank. Each head has an annular surface portion that is defined at the transition between the head and shank and bounds the blade working space either directly or indirectly, in the event that a washer is placed against the head.
The shanks each extend through registered slots in the separate blades. The slots extend lengthwise of the blade. Through this arrangement, the blades can be translated back and forth in a path that aligns generally with the length of the blades with the shanks guiding this movement.
The blades are designed with a uniform thickness so that they together occupy a combined thickness that is slightly less than the spacing between the aforementioned fixed surfaces bounding the blade working space. This allows facing surfaces on the blades and support to be slid guidingly, one against the other, as the trimming apparatus is operated.
Different structures have been utilized to maintain the depth of the working space between the fixed surfaces. In one form, headed spacer unit bodies are directed through the blades and threaded into the support. By turning the bodies, the heads can be drawn towards the support surface. By initially fully tightening the bodies and thereafter turning the same in a loosening direction, a slight gap can be created and maintained to allow guided, but relatively unimpeded, relative movement between the blades and support.
It is also known to make spacer units with a spacer block through which a shank extends. The spacer block becomes captive between a head and the support so that the depth of the blade working space is determined by the thickness of the block. The use of the blocks allows a relatively small diameter shank to be utilized while at the same time consistently maintaining a predetermined depth for the working space without requiring any judgment or adjustment on the part of the manufacturer or user.
Because the blades and support have surfaces that are guided, one against the other, the blades are prone to wearing through frictional abrasion. As a result, the thicknesses of the blades may vary, as a result of which they fit loosely within the depth of the blade working space. This may cause vibration as the unit is operated and further may result in improper alignment of the cutting edges so that the cutting ability of the apparatus is compromised. This condition could cause blade jamming and potentially parts failure.
Typically, the abrasive wear is non-uniform over the length of the blades. The free end region is more prone to wearing, and thus the blades tend to thin more extensively thereat.
Parts and kits are offered to users of this type of apparatus to allow them to locally change the depth of the blade working space once this wear occurs. For example, spacer blocks may be provided with a reduced thickness and can be substituted for the originally assembled spacer blocks in the regions where there is appreciable wear. This approach is effective only if the replaced spacer blocks can be substituted for by spacer blocks with the appropriate thickness. If only a single replacement block thickness is available, it may not be matched to the new combined thickness of the worn blades. If multiple blocks are offered with different thicknesses, a user may have to use a trial and error process to select the appropriate block.
An additional problem with this construction is that one or more washers may additionally have to be provided as part of the spacer unit. Thus, a user must handle and assemble multiple parts, which may become inconvenient to the point that a user will forego any modification of the trimming apparatus and use the same with the blades significantly worn. This may give the user a bad perception of the product, which may cut ineffectively and eventually fail due to the play that results from the thinning of the blades.
The industry continues to seek designs that are not only effective at time of initial construction, but which can be simply modified by a user to allow optimal operation through the anticipated lifetime of the apparatus.